1. Field of the Invention
The invention relates to a cutter hub holder for blades acting against a die plate of an underwater pelletizer including a spring-loaded blade holder that is drivingly connected with a driven shaft and biased axially toward the die plate at a variable controlled pressure. The driving connection of the cutter hub holder between the shaft and blade holder includes a quick connect and disconnect drive coupling.
2. Description of the Prior Art
The following U.S. patents relate to developments in underwater pelletizers.
______________________________________ 3,196,487 4,529,370 5,110,523 3,317,957 4,614,307 5,190,768 4,123,207 4,728,276 5,435,713 4,179,255 5,059,103 5,527,176 4,500,271 ______________________________________
The above patents disclose (a) an arrangement that manually controls displacement of the cutter assembly to compensate for blade wear and maintain the proper blade-to-die pressure, (b) an arrangement that automatically advances the blade by a stepping motor activated by a sensor that detects blade wear by sensing the relative distance between the cutter assembly and the die, (c) a spring that exerts pressure against the knife holder assembly and (d) electronic circuits for controlling hydraulic pressure to automatically displace the drive shaft and thereby control blade-to-die pressure. However, the above patents do not disclose a structure which delivers variable pneumatic pressure to a piston and cylinder incorporated into the drive shaft to an intermediary member which, in turn, exerts a force against a spring that displaces the cutter assembly or cutter hub to maintain optimum pressure of the cutter blades toward the die face. Also, the above patents do not disclose a bayonet coupling cutter hub attachment to the drive shaft of an underwater pelletizer which permits relative axial movement therebetween.
In a cutter hub holder of this type, such as generally disclosed in U.S. Pat. No. 5,059,103 issued Oct. 22, 1991, the cutter hub is pressed against the die plate by a spring, in order to compensate for wear of the cutting blades and to ensure a permanent contact of the cutting blades with the die plate. In the known cutter hub holders the spring pressure is selected to satisfy the needs during pelletizing. This pressure force is thus always set to the highest pressure required during operation, while there are phases in operations during which a lower spring force would be sufficient. Yet, the higher the spring pressure acting on the blade holder, the greater the wear of the blades and of the die plate.
Any equipment utilizing manual adjustment methods for the cutter holder and blades requires considerably more operator attention while the equipment is running. As the blades wear, the pellet quality decreases causing the operator to constantly monitor the process and adjust the blades. The amount of adjustment that is made will vary from one operator to the next. Often the tendency is to over adjusts causing premature blade and die wear. The invention being proposed uses constants controllable pneumatic pressure to continually adjust the cutter blades. The pressure can be set as light or as heavy as required allowing the operator to move one setting with no further adjustment required. A compression spring is used in the cutter head to assure constant contact between the die and cutter.
Any equipment utilizing a compression spring alone to adjust the blades offers no flexibility for varying the pressure of the cutter blades against the die face. A spring of the desired tension must be installed in the cutter head during setup. Once the machine is running, the spring tension cannot be varied, even though a heavier or lighter spring may be required. The entire cutting process must be stopped if the spring is to be changed. With a controllable pneumatic pressure, as proposed by the instant invention, the blade to die pressure can be adjusted as light or as heavy as required with a simple air pressure regulator.
Any equipment utilizing hydraulic pressure to adjust the blades requires the use of a dedicated hydraulic power unit for controlling the blade to die pressure. The use of this method to control blade adjustment is much more involved, both mechanically and electrically. Provisions must be made on or around the equipment to house a hydraulic power unit, whereas with a pneumatic design, installing an air line is all that is required. In environments where equipment of this nature is installed, compressed air lines are commonly available. A designated control circuit is also required on the hydraulically adjusted unit for the drive motor on the hydraulic power unit. Also, when using the hydraulic method, special care must be taken to prevent hydraulic oil from leaking into the process water, even in the event of a seal failure.